EP1279968A2 - Bobine émettrice-réceptrice pour appareil de résonance magnétique - Google Patents

Bobine émettrice-réceptrice pour appareil de résonance magnétique Download PDF

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Publication number
EP1279968A2
EP1279968A2 EP02100495A EP02100495A EP1279968A2 EP 1279968 A2 EP1279968 A2 EP 1279968A2 EP 02100495 A EP02100495 A EP 02100495A EP 02100495 A EP02100495 A EP 02100495A EP 1279968 A2 EP1279968 A2 EP 1279968A2
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EP
European Patent Office
Prior art keywords
resonator
segments
segment
arrangement according
resonator segment
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP02100495A
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German (de)
English (en)
Other versions
EP1279968A3 (fr
Inventor
Christoph Leussler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Philips Intellectual Property and Standards GmbH
Koninklijke Philips NV
Original Assignee
Philips Intellectual Property and Standards GmbH
Philips Corporate Intellectual Property GmbH
Koninklijke Philips Electronics NV
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Publication date
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Publication of EP1279968A2 publication Critical patent/EP1279968A2/fr
Publication of EP1279968A3 publication Critical patent/EP1279968A3/fr
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/5659—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/34046—Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/34046—Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
    • G01R33/34076—Birdcage coils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
    • G01R33/3628—Tuning/matching of the transmit/receive coil

Definitions

  • the invention relates to an arrangement for generating high-frequency fields in the unexplored volume of an MR device, with a body coil consisting of a plurality of resonator segments, the resonator segments being arranged around the examination volume and each comprising at least one conductor element running parallel to the longitudinal axis of a main field magnet and at least one consist of a capacitor element.
  • the high-frequency system of conventional MR devices includes a transmitting and receiving coil, such as an integrated body coil, which can be used for the volume imaging of the examination volume.
  • a transmitting and receiving coil such as an integrated body coil
  • phased array coils can also be used to achieve an improved reception quality (improved signal-to-noise ratio, higher resolution).
  • the body coils used both for excitation and for the detection of MR signals are usually so-called cage resonators (birdcage coil). These consist of a plurality of conductor bars arranged around the unevenness volume and running parallel to the main field direction, which are connected to one another on the end faces of the coil via ring conductors.
  • the resonance behavior of the body coil is determined by capacitor elements, by means of which the conductor elements are connected to form a network.
  • the first resonance mode (basic mode) of these resonators is distinguished by a homogeneous B 1 field distribution in the entire interior of the resonator.
  • the body coil in volume imaging is usually operated in the transmit mode in the basic mode. It is also possible to control the resonator in such a way that orthogonal, that is to say decoupled, resonances would be excited at the same frequency, which is used for quadrature detection.
  • the nuclear magnetization is localized within the examination volume by means of spatially inhomogeneous magnetic fields (magnetic field gradients) that change over time.
  • the nuclear spin signal is recorded as a voltage, which is induced in the body coil surrounding the examination volume, under the influence of a suitable sequence (sequence) of high-frequency and gradient pulses in the time domain.
  • sequence sequence of high-frequency and gradient pulses in the time domain.
  • the actual image reconstruction then takes place by Fourier transformation of the time signals.
  • the number, the time interval, the duration and the strength of the gradient pulses used determine the scanning of the reciprocal k-space, by means of which the volume range to be imaged (FOV, "field of view") and the image resolution are determined by requirements for the image size and image resolution, the number of phase encoding steps and thus the duration of the imaging sequence is specified.
  • FOV volume range to be imaged
  • image resolution are determined by requirements for the image size and image resolution, the number of phase encoding steps and thus the duration of the imaging sequence is specified.
  • image generation with the highest possible resolution is sought in the shortest possible time. This places special demands on the gradient system of the MR devices, whereby the fastest possible switching of the strongest possible magnetic field gradients is to be achieved.
  • the gradient system is usually accommodated in a so-called gradient tube, which surrounds the uncovered volume.
  • a high-frequency shielding (HF shield) is arranged between the gradient tube and the body coil, by means of which interference signals from the surroundings of the examination volume are prevented on the one hand and on the other hand radiation of high-frequency power into the surroundings of the MR device is prevented.
  • An increase in the gradient field strength can be achieved, for example, by reducing the diameter of the gradient tube. If the examination volume and the inner diameter of the body coil are retained, the distance between the high-frequency shielding and the body coil is reduced at the same time.
  • the small distance between the conductor elements of the body coil and the high-frequency shielding results disadvantageously in a reduction in the B 1 field strength or the detection sensitivity in the inner region of the coil. This has the undesirable consequence that the required transmission power increases and the signal-to-noise ratio decreases at the same time.
  • the reduction in the tube diameter also has a disadvantageous effect on the resonance behavior of the body coil, since the frequency spacings between the individual resonance modes become too small, which results in an undesired mode coupling arises.
  • an increase in the gradient field strength can be achieved by using a gradient tube with an asymmetrical cross section.
  • this also requires the use of asymmetrical body coils.
  • Such asymmetrical resonator arrangements lead to a number of problems in practice. On the one hand, it is difficult to orthogonalize such a body coil in order to make quadrature operation possible.
  • the high-frequency field profile in the coil interior is dependent on the current distribution in the arrangement of the conductor elements, which is why the homogeneity of the high-frequency field in transmit mode and corresponding to the spatial sensitivity profile in receive mode is generally unsatisfactory in the case of asymmetrical resonators.
  • the present invention is based on the object of providing an improved HF transmission and reception arrangement for MR devices, which can be used for any, in particular also for small and asymmetrical, tube diameters. At the same time, sufficient homogeneity and easy-to-handle resonance behavior should be provided.
  • this object is achieved in that the resonator segments are electromagnetically decoupled from one another and in that each resonator segment is assigned a separate transmission channel via which the HF feed into the relevant resonator segment takes place, with the phase and for each resonator segment / or the amplitude of the HF feed can be specified individually.
  • the field distribution in the examination volume can advantageously be completely controlled. It is in fact possible to generate any conceivable current distribution in the arrangement of the conductor elements by specifying the amplitude and phase on the individual transmission channels.
  • the timing of the RF feed can also be specified individually on each transmission channel.
  • the amplitude and the phase of each individual transmission channel can be controlled by the software of the MR device, which enables direct interactive control of the field distribution (RF shimming). It is conceivable, for example, to integrate a fully automatic regulation of the RF field homogeneity in the imaging sequence in order to compensate for variable influences on the field distribution, for example due to the different dielectric properties of the examined patients.
  • the only requirement is that the individual resonator segments are electromagnetically decoupled from one another.
  • the body coil must therefore have a resonance behavior which ensures that the individual resonator segments vibrate independently of one another at the desired resonance frequency.
  • coil arrangements are known in which at least immediately adjacent resonator segments are decoupled from one another.
  • additional means must be provided by means of which the electromagnetic couplings are also minimized between more distant resonator segments. In practice it has been shown that mutual isolation of the resonator segments of approximately -20 dB is desirable to prevent crosstalk between the individual transmission channels as much as possible.
  • the mutual electromagnetic decoupling of the resonator segments can be carried out particularly easily according to claim 2 by means of capacitors or inductors arranged between the conductor elements. Appropriate dimensioning of the capacitance or inductance values must ensure that there is no resonant coupling between the different resonator segments. It can be useful to provide decoupling networks (consisting of capacitors and inductors) between the conductor elements of both adjacent and more distant resonator segments.
  • the conductor elements are designed as essentially rectangular, area-like strips. It can be seen that when flat conductor strips are used, the magnetic couplings between more distant resonator segments are weakened.
  • the body coil can be realized in a particularly space-saving manner using the flat conductor strips.
  • the current distribution within the strip-shaped conductor elements can be easily influenced, for example by introducing holes or cutouts or by structuring the edges of the conductor strips in a suitable manner.
  • the use of flat conductor strips leads to an areal current distribution within the conductor elements, whereby an improved local field homogeneity is achieved.
  • the field strength in the examination volume is weakened by the HF shield, which is located between the gradient tube and the body coil, which is why the greatest possible distance between the coil arrangement and the HF shield must usually be maintained.
  • the conductor elements of the individual resonator segments it is expedient to arrange the conductor elements of the individual resonator segments at a short distance from the RF shield. Because of the proximity to the HF shield, the mutual magnetic coupling between the individual conductor elements is reduced, which is advantageous for the resonance behavior of the body coil in the sense of the invention.
  • the distance between the conductor elements and the HF shield may be expedient to choose the distance between the conductor elements and the HF shield such that, on the one hand, there is sufficient magnetic decoupling between the Conductor elements is reached and that, moreover, the high-frequency field strength in the examination volume is not reduced too far.
  • the possibility of being able to specify the spatial distribution of the high-frequency field in the examination volume as desired with the arrangement according to the invention opens up a number of further fields of application. For example, gradients in the high-frequency field can be generated in different spatial directions.
  • the excited nuclear magnetization distribution can be given a location code that can be used for fast volume imaging (transmit-SENSE method).
  • a spatially selective presaturation of the nuclear magnetization in the examination volume is also conceivable.
  • the body coil is divided into at least two independent sections arranged one behind the other in the axial direction.
  • the high-frequency field distribution in the main field direction (z-direction) in particular high-frequency field gradients along the z-axis being possible
  • each resonator segment via which the MR signals detected by means of the relevant resonator segments are transmitted to a receiving unit for further processing.
  • a separate reception channel to each resonator segment, via which the MR signals detected by means of the relevant resonator segments are transmitted to a receiving unit for further processing.
  • the MR signals detected by means of the individual resonator segments Signals to perform volume imaging with a spatially homogeneous sensitivity profile.
  • partial images can be generated from the separately detected MR signals, which are then combined with one another to form an overall image.
  • this can be advantageous for improving the signal-to-noise ratio, the individual resonator segments being used as synergy coils.
  • the individual images as a basis to combine spatial sensitivity profiles assigned to the individual resonator segments with one another in order to save measurement time in imaging (SENSE method).
  • the arrangement according to the invention advantageously allows the examination volume in the plane running perpendicular to the main field direction to have an asymmetrical cross section, on the peripheral edge of which the guide elements of the individual resonator segments are arranged. Due to the fact that the high-frequency field distribution in the unexamination volume can be controlled almost arbitrarily, even with such an asymmetrical geometry of the body coil, sufficient homogeneity of both the excitation field and the spatial sensitivity profile can be ensured during the detection. As mentioned, asymmetrical examination volumes have the advantage that particularly high magnetic field gradients can be achieved.
  • each transmission channel is connected to an output of a connection network (combiner hybrid) assigned to the resonator segment in question, by means of which the power of a transmission amplifier is distributed to the individual resonator segments.
  • the phase and the amplitude of the respectively fed-in HF signal are determined by the connection network for each resonator segment.
  • This embodiment has the advantage that only a single power transmitter is required for high-frequency radiation, the output signal of which is distributed to the individual resonator segments by means of the combiner hybrid.
  • the distribution is expediently carried out in such a way that the most homogeneous high-frequency field distribution is generated in the examination volume. It is expedient if, according to claim 12, a measuring element (pick-up coil) is assigned to at least one, but preferably to each resonator segment, via which the RF field strength emitted by the respective resonator segment is determined, the measurement signal being sent to the control unit of the MR device Monitoring and / or for regulating the phase and the amplitude of the fed RF signal is supplied.
  • a measuring element pick-up coil
  • an examination volume 100 In the center of the MR device shown in FIG. 1 is an examination volume 100, in which a patient 102 is located on a patient table 101.
  • a static magnetic field with a strength of, for example, 1.5 Tesla is generated by means of a main field magnet (not shown in more detail).
  • main field magnet not shown in more detail.
  • time-varying magnetic field gradients must also be generated in the examination volume 100.
  • gradient coils are used for this purpose, which are accommodated in a gradient tube 103 surrounding the examination volume 100.
  • the gradient tube 103 has an asymmetrical cross section, which, as described above, is conducive to achieving the greatest possible gradient field strengths.
  • the generation of high-frequency fields takes place by means of resonator segments arranged within the gradient tube 103 around the examination volume 100 and consisting of parallel to the longitudinal axis of the main field magnet extending flat, strip-shaped conductor elements 104 exist.
  • the conductor elements 104 are networked with one another and possibly also against ground via capacitor elements, as a result of which the resonance behavior of the arrangement is determined.
  • the capacitor elements form the body coil of the MR device, which is used not only to excite nuclear magnetic resonance signals in the examination volume 100, but also to detect them.
  • An RF screen 105 surrounding the entire examination volume 100 is located between the gradient tube 103 and the conductor elements 104 of the body coil.
  • Each of the eight conductor elements 104 shown in FIG. 1 is connected to a changeover switch S through which the conductor element 104 in question is connected to one of two possible connections, depending on the operating mode.
  • the connections intended for the transmission mode are designated with the numbers 1-8, the connections intended for the reception mode with the lower case letters ah.
  • the connections 1-8 are assigned the outputs with the corresponding numbers of a transmission unit 106. This has a separate transmission channel for each individual resonator segment of the body coil, which each has a power amplifier 107 and a high-frequency control unit 108.
  • the amplitude and phase of the high-frequency signal can be set individually for each individual transmission channel by means of the high-frequency control unit 108, so that almost any high-frequency field distribution in the examination volume 100 of the MR device can be generated.
  • a distribution network 109 (combiner hybrid), through which the output signal of a high-frequency transmission amplifier 110 is distributed to the connections 1-8, with the combiner hybrid for each output channel 1-8 the amplitude and phase of the radio frequency signal is determined.
  • the transmission unit 106 or the transmission amplifier 110 is connected to a control unit 111.
  • the control unit 111 is also connected to the gradient tube 103.
  • the reception channels designated with the corresponding letters ah are assigned to the connections ah intended for the reception operation of a reception unit 112.
  • Each receiving channel has a sensitive high-frequency preamplifier 113 and a demodulator 114 equipped.
  • the MR signals registered by the receiving unit 112 are transmitted to a reconstruction unit 115, where the digitized signals are combined with one another and Fourier analyzed.
  • the images generated by the reconstruction unit 115 are then output on the monitor of a microcomputer 116.
  • the microcomputer 116 also serves to control the MR device by a user, for which purpose the computer 116 is also connected to the control unit 111.
  • surface coils 117 lying directly on the body of the patient 102 can also be used, which are connected to the corresponding inputs of the receiving unit 112 via the connections i and j.
  • the surface coils 117 can be used, for example, for local cardiac imaging, the conductor elements 104 of the body coil (connections g and h) arranged in the back area of the patient 102 being used together with the surface coils 117 in synergy operation for data acquisition.
  • FIG. 2 shows a conventional cage resonator in which the ring capacitances C T and the rod capacitances C A are selected such that the resonator operates in a decoupled mode at the desired resonance frequency (cf. Leussler et al., Proceedings of the ISMRM, No. 176, Vancouver 1997).
  • a resonator can be used with any diameter and cross section (symmetrical or asymmetrical) according to the invention.
  • the immediately adjacent resonator segments are sufficiently decoupled from one another due to the special resonance mode of the resonator.
  • the couplings between more distant segments are too high for the resonant transmission mode.
  • the individual conductor bars 104 can be isolated from one another by means of suitable impedance networks. Such decoupling from neighbors after next may be sufficient. It is also beneficial for the decoupling to choose a comparatively small distance between the resonator and the HF shield, even if this slightly reduces the high-frequency field strength in the examination volume.
  • the rods 104 running parallel to the main field direction can also be designed as flat conductor strips. In this version of the resonator, with capacitances in the rods or strips, no current flows through the HF shield due to the galvanic isolation.
  • the resonator is designed in such a way that the distance between the RF shield and the conductor strips 104 changes along their longitudinal extent, the distance to the HF shield being greater at the front ends of the resonator than in the central region. This improves the homogeneity of the RF field in the examination volume.
  • FIGS. 3, 4 and 5 show flat representations of body coils according to the invention.
  • the coils consist of a plurality of flat conductor strips 104 which are arranged around the examination volume.
  • the resonance frequency of the individual resonator segments is determined by the capacitors connected to ground in FIGS. 3 and 4. 5, the resonance frequency is determined by the capacitances C R arranged in the conductor strips and the capacitances C G connected to ground.
  • Such an arrangement is particularly advantageous in order to avoid electromagnetic propagation effects at high resonance frequencies.
  • a number of capacitances C R connected in parallel are used within the conductor strips in order to divide the high currents during transmission and to achieve a uniform current distribution, which is advantageous for the homogeneity of the high-frequency field.
  • each individual conductor element 104 is connected to a transmission channel 1, 2, 3 or 4 via an intermediate capacitor (FIGS. 3, 5).
  • FIG. 6 shows different designs of conductor strips 104, in which different structures are provided in order to achieve a current distribution that is as homogeneous as possible. For this purpose, it is particularly expedient to increase the edge impedance of the conductor strips by means of one of the sawtooth-like edge structures shown. Convex or concave designs of the conductor strips 104 or the provision of slots 601, which can be bridged by capacitors 602, are also conceivable.
  • FIG. 7 shows the implementation of the mutual electromagnetic decoupling of the next resonator segments 104. Since the corresponding conductor strips 104 are not located directly next to one another, they are connected with coaxial cables of suitable length ( ⁇ / 2 or ⁇ / 4). A suitable impedance network Z then effects the desired insulation. The aim is to feed the signal to the other resonator segment via the impedance network Z in such a way that compensation of the directly coupled high-frequency signal is achieved by the appropriate specification of the amplitude and by the corresponding shift in the phase. Such decoupling can of course also be used equally for immediately adjacent and for distant segments of the resonator. In the simplest case, the impedance network Z can consist of a capacitor, via which the resonator segments in question are connected, or of an inductance connected to ground.
  • FIG. 8 shows an interleaved arrangement of conductor elements which, according to the invention, are decoupled from one another by intermediate capacitances C D and interconnected to form a body coil.There are thus two independent sections of the body coil arranged one behind the other in the axial direction, which are used to control the high frequency -Field distribution in the direction parallel to the longitudinal axis of the main field magnet (z direction) can be used.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
EP02100495A 2001-05-19 2002-05-15 Bobine émettrice-réceptrice pour appareil de résonance magnétique Withdrawn EP1279968A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE10124465 2001-05-19
DE10124465A DE10124465A1 (de) 2001-05-19 2001-05-19 Sende- und Empfangsspule für MR-Gerät

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EP1279968A2 true EP1279968A2 (fr) 2003-01-29
EP1279968A3 EP1279968A3 (fr) 2004-05-06

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US (1) US6900636B2 (fr)
EP (1) EP1279968A3 (fr)
JP (1) JP4004964B2 (fr)
DE (1) DE10124465A1 (fr)
WO (1) WO2002095435A1 (fr)

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DE102005017310A1 (de) * 2005-04-14 2006-10-26 Siemens Ag Magnetresonanzeinrichtung umfassend eine vorzugsweise zylindrische Körperspule zur Erzeugung eines homogenen hochfrequenten Magnetfelds sowie Verfahren zum Erzeugen eines homogenen hochfrequenten Magnetfelds
US7221162B2 (en) 2003-11-19 2007-05-22 Siemens Aktiengesellschaft RF transmitter arrangement for an MR system, and method for determining a setting parameter therefor
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US7733088B2 (en) 2007-11-22 2010-06-08 Gachon University Of Medicine & Science Industry - Academic Cooperation Foundation MRI system RF coil assembly with a birdcage transmit only coil and a pseudo-chain-link receive only coil array
WO2014064573A1 (fr) 2012-10-25 2014-05-01 Koninklijke Philips N.V. Bobine en cage d'oiseau radiofréquence (rf) avec des éléments d'anneau et des barreaux commandés séparément pour une utilisation dans un système d'imagerie à résonance magnétique (mr)

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EP1581818A2 (fr) 2002-11-27 2005-10-05 Koninklijke Philips Electronics N.V. Degenerescence d'un enroulement en cage d'oiseau et emetteur/recepteur et procede correspondant
WO2004053514A1 (fr) * 2002-12-06 2004-06-24 Koninklijke Philips Electronics N.V. Systeme d'imagerie par resonance magnetique dote d'une pluralite de bobines de transmission
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AU2004277703A1 (en) * 2003-10-03 2005-04-14 Regents Of The University Of Minnesota Parallel transceiver for nuclear magnetic resonance system
CN100578250C (zh) 2003-11-18 2010-01-06 皇家飞利浦电子股份有限公司 用于mri的混合tem/鸟笼型线圈
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US7053618B2 (en) * 2003-11-26 2006-05-30 General Electric Company Method and apparatus to generate an RF excitation consistent with a desired excitation profile using a transmit coil array
GB2409522B (en) * 2003-12-22 2006-10-18 Ge Med Sys Global Tech Co Llc Gradient coil apparatus and method of assembly thereof
DE102004002009B4 (de) * 2004-01-14 2006-07-06 Siemens Ag Verfahren zum Betrieb eines Magnetresonanzsystems, Magnetresonanzsystem und Computerprogrammprodukt
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DE102004013422B4 (de) * 2004-03-18 2009-02-19 Siemens Ag Verfahren zur Homogenisierung eines B1-Felds, Magnetresonanzsystem und Computerprogrammprodukt
AU2005242783A1 (en) * 2004-05-07 2005-11-24 Regents Of The University Of Minnesota Multi-current elements for magnetic resonance radio frequency coils
EP1751570A1 (fr) * 2004-05-14 2007-02-14 Koninklijke Philips Electronics N.V. Bobine tem a elements courts pour resonance magnetique a champ ultra-eleve
WO2005124379A1 (fr) * 2004-06-18 2005-12-29 Koninklijke Philips Electronics, N.V. Bobine hf cage d'oiseau a faible taux d'absorption specifique local
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US6900636B2 (en) 2005-05-31
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US20040155656A1 (en) 2004-08-12
JP4004964B2 (ja) 2007-11-07

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